This invention relates to the provision of novel methylaluminoxane compositions, to especially useful solutions of such methylaluminoxanes in hydrocarbon solvents other than aromatic hydrocarbon solvents, and to the preparation of such compositions and solutions.
In the ensuing description and in the claims hereof, reference is sometimes made to solubility in n-heptane because this is a typical, representative saturated hydrocarbon which serves as a very convenient point of reference for comparisons of solubility. However, such references to n-heptane does not constitute a limitation or restriction on the scope of this invention as regards hydrocarbons used, as the invention produces methylaluminoxane compositions that have improved solubility in a variety of liquid aliphatic and cycloaliphatic hydrocarbons as compared to the solubility of previously reported methylaluminoxane in the same respective hydrocarbons.
Hydrocarbylaluminoxanes complexed with transition metal compounds are known to be effective olefin polymerization catalysts. See for example, U.S. Pat. No. 3,242,099 to Manyik et al. Methylaluminoxanes prepared by partial hydrolysis of trimethylaluminum under various conditions are commonly-used effective co-catalyst components. However as is well known, methylaluininoxanes have been found to have poor solubility in non-aromatic hydrocarbon solvents. See in this regard, U.S. Pat. Nos. 4,960,878 to Crapo et al.; 5,041,584 to Crapo et al.; 5,066,631 to Sangokoya et al.; 5,308,815 to Sangokoya; 5,847,177 to Sangokoya et al.; 6,001,766 to Kissin et al., and Japan Kokai 01/258,686 to Kioka et al.
Disclosures from which it is possible to calculate or at least estimate total aluminum concentrations in non-aromatic solvents include U.S. Pat Nos. 4,530,914 to Ewen et al.;
U.S. Pat. No. 4,544,762 to Kaminsky et al.; U.S. Pat. No. 4,701,432 to Welborn; U.S. Pat. No. 4,752,597 to Turner; U.S. Pat. No. 4,791,180 to Turner; and U.S. Pat. No. 5,066,631 to Sangokoya et al.; and Ott, University of Hamburg Thesis, 1999. It appears that the highest reported total aluminum concentration in these documents is 3.85 wt % in heptanexe2x80x94see Example 3 of U.S. Pat. No. 5,066,631 to Sangokoya et al. It appears from an abstract of a paper by Matthias Ott, entitled Optimization of Methylaluminoxane Preparation, Fortschr.-Ber. VDI Reihe 3 (1999),627, I-III, V-XVI, 1-137 (Accession number 2000:106460 CAPLUS) that it is speculated that it will be possible to prepare methylaluminoxane solutions of up to 10% in heptane with the use of the xe2x80x9cEisbandreaktorxe2x80x9d referred to therein.
The poor solubility of methylaluminoxanes in non-aromatic solvents is most unfortunate because polyolefin manufacturers of products that come into contact with foodstuffs desire to minimize as much as possible, if not eliminate, aromatic hydrocarbons from the raw materials and processing operations used. The manufacturers would much prefer raw materials and operations in which less toxic non-aromatic hydrocarbons are employed.
Considerable past efforts have been devoted to various ways of modifying methylaluminoxanes in order to increase their solubility in non-aromatic hydrocarbons. These efforts generally involve either the addition or inclusion of other components to improve such solubility, or the treatment of the methylaluminoxane in such a way that a substantial portion of methylaluminoxane, e.g., at least 25 percent by weight of the total methylaluminoxane on a dry basis, exists or remains as a precipitate and is not included in the solution. Such precipitates are believed -to be composed of higher molecular weight oligomers and are isolated by filtration, decantation, or other liquid-solids physical separation procedure.
Whatever their makeup, such precipitates are usually discarded as waste, thereby leaving in solution a lower molecular weight methylaluminoxane fraction which generally contains more than about 30 mole percent trimethylaluminum and is more soluble in non-aromatic solvents. A number of examples of such approaches are described in the patent literature.
It would be of considerable advantage if a way could be found of providing new methylaluminoxane compositions having superior solubility characteristics in various non-aromatic hydrocarbons, especially paraffinic and cycloparaffinic hydrocarbons, without need for (a) addition or inclusion of other components to improve such solubility, or (b) treatment of the methylaluminoxane in such manner that results in loss of a substantial portion of its original content.
This invention involves, inter alia, the discovery that it is indeed possible to form and provide such new methylaluminoxane compositions having significantly higher solubility in non-aromatic hydrocarbons without addition of any third component to increase solubility, and without recourse to processing that removes substantial portions of higher molecular weight components from the methylaluminoxane.
Accordingly, in one of its embodiments this invention provides a methylaluminoxane composition wherein:
A) the composition is a solid at 25xc2x0 C.;
B) the composition has a total aluminum content in the range of about 39 to about 47 wt % based on the total weight of the composition in the solid state;
C) the composition is either free of aluminum in the form of trimethylaluminum or if trimethylaluminum is present in the composition, not more than about 30 mole %, preferably no more than about 20 mole %, and most preferably no more than about 10 mole % of the total aluminum present in the composition is in the form of trimethylaluminum;
D) the composition in the solid state contains no more than about 2000 ppm (wt/wt) of aromatic hydrocarbon;
E) the cryoscopic number average molecular weight of the composition as determined in benzene is at least-about 1000, preferably at least about 1100, and more preferably at least about 1200 atomic mass units; and
F) the composition has sufficient solubility in n-heptane at 25xc2x0 C. to provide a solution containing at least 4 wt %, preferably at least 5 wt %, and most preferably at least 7.5 wt % of dissolved aluminum.
Another embodiment of this invention is a method of preparing the above 5 methylaluminoxane compositions. The method comprises subjecting a solution of methylaluminoxane in an aromatic hydrocarbon solvent to distillation at a temperature no higher than about 25xc2x0 C. under reduced pressure of below 1xc3x9710xe2x88x925 millimeters of mercury to form a solid methylaluminoxane composition that complies with each of the criteria set forth above as A) through F), inclusive.
Pursuant to another embodiment of this invention there is provided a composition which comprises a solution of methylaluminoxane in a non-aromatic hydrocarbon solvent, wherein:
a) if any trimethylaluminum is present in the solution, no more than about 30 mole %, preferably no more than about 20 mole %, and more preferably no more than about 10 mole % of the total dissolved aluminum in the solution is trimethylaluminum;
b) the solution has a total dissolved aluminum content above 4 wt %, preferably 5 wt % or more, and more preferably at least about 7.5 wt %, based on the total weight of all dissolved aluminum components of the methylaluminoxane plus the weight of the non-aromatic hydrocarbon solvent;
c) the solution contains, if any, no more than 2000 ppm (wt/wt) of aromatic hydrocarbon, based on the total weight of all dissolved aluminum components of the methylaluminoxane plus the total weight of the hydrocarbon solvent (i.e., including the weight of the aromatic hydrocarbon, if any, in the solution); and
d) the methylaluminoxane in the solution has a cryoscopic number average molecular weight as determined in benzene of at least 1000, more preferably at least 1100, and most preferably at least 1200 atomic mass units.
Still another embodiment of this invention is a method of preparing the compositions of the immediately preceding paragraph. The method comprises subjecting a solution of methylaluminoxane in an aromatic hydrocarbon solvent to distillation at a temperature no higher than about 25xc2x0 C. under reduced pressure of about 1xc3x9710xe2x88x925 millimeters of mercury or less to form a solid methylaluminoxane residue that has (i) an aluminum content in the range of about 39 to about 47 wt %, (ii) a trimethylaluminum content, if any, of no more than about 30 mole %, preferably no more than about 20 mole %, and more preferably no more than about 10 mole % of the total aluminum content of the residue, and (iii) a cryoscopic number average molecular weight as determined in benzene of at least 1000, more preferably at least 1100, and most preferably at least 1200 atomic mass units; and dissolving such solid methylaluminoxane residue in a non-aromatic hydrocarbon solvent in an amount such that the resultant solution contains at least 4 wt %, preferably at least about 5 wt %, and more preferably at least about 7.5 wt % of dissolved aluminum based on the weight of these specified components.
The method to be used in determining the mole percentage of trimethylaluminum in the methylaluminoxane, in any case where it is desired or deemed necessary to determine such mole percentage, is identified hereinafter and is referred to in this document as the NMR Analytical Procedure. It is described in xe2x80x9cCharacterization of Methylaluminoxanes and Determination of Trimethylaluminum Using Proton NMRxe2x80x9d by Donald W. Imhoff, Larry S. Simeral, Samuel A. Sangakoya, and James H. Peel; Organometallics, 1998, 17, 1941-1945.
These and other embodiments and features of this invention will become further apparent from the ensuing description and appended claims.
The methylaluminoxanes (a.k.a. methylalumoxanes) components utilized as starting materials in forming the aromatic hydrocarbon solution prior to distillation are essentially the same as those made commercially in aromatic solvents (e.g. toluene). They are characterized by evolving, when subjected to hydrolysis with water, methane, as well as very small amounts of hydrogen and hydrocarbon molecules which are larger than methane, such as, for example, ethane, propane, isobutane and n-butane. These alkanes larger than methane result from impurities in the trimethylaluminum from which the methylaluminoxane is produced. No organoaluminum compound other than trimethylaluminum of typical commercial purity (e.g., 98% or more) should be used in forming or be added to the methylaluminoxane starting material.
Either of two different types of processes are usually, but not necessarily, used for producing the methylaluminoxanes used as starting materials in the practice of this invention. One such well-known process involves controlled, partial hydrolysis of trimethylaluminum with free water or with water derived from a hydrated metal salt. Processes of this type are described, for example, in U.S. Pat. Nos. 4,908,463; 4,924,018; 5,003,095; 5,041,583; 5,066,631; 5,099,050; 5,157,008; 5,157,137; 5,235,081; 5,248,801, and 5,371,260. Methyl-aluminoxanes typically contain varying amounts, of from about 5 to 35 mole percent, of the aluminum value as unreacted trimethylaluminum. Preferably, the aluminum content as trimethylaluminum is less than about 23 mole percent of the total aluminum value, and, more ipreferably, less than about 20 mole percent. The other process involves treating trimethylaluminum with a compound containing an oxygen-carbon bond such as carbon dioxide, benzoic acid, benzophenone, acetone and the like. See in this connection, U.S. Pat. No. 5,831,109, entitled xe2x80x9cPolyaluminoxane Compositions Formed by Non-Hydrolytic Meansxe2x80x9d.
Often the methylaluminoxane as produced and offered for sale in the marketplace is in the form of a solution in an aromatic hydrocarbon, typically toluene. Such solutions usually contain 10 or 30 wt % of the methylaluminoxane, and it is convenient (but of course not necessary) to use such solutions in preparing the new methylaluminoxane compositions of this invention.
A solution of the conventional methylaluminoxane in an aromatic hydrocarbon solvent is subjected to distillation under reduced pressure conditions at a temperature no higher than about 30xc2x0 C. for a period of time long enough not only to remove the liquid phase but to produce a solid product satisfying the above criteria of A) through F) inclusive. Preferably the distillation is performed at ambient room temperature, e.g., at temperatures in the vicinity of 25xc2x0 C. The pressure during distillation is maintained below about 1xc3x9710xe2x88x925 millimeters of mercury, with a pressure of less than about 5xc3x9710xe2x88x926 millimeters of mercury being more desirable. The time period for the vacuum distillation will of course vary depending upon such factors as the concentration of the initial solution of the methylaluminoxane, the aromatic hydrocarbon used as the solvent for such solution, and the reduced pressure employed. Times in the range of about 4 to about 120 hours may suffice, but in any case where suitable or optimal time-temperature-pressure conditions for any given initial aromatic hydrocarbon solution of methylaluminoxane have not been previously ascertained, a few pilot experiments on a laboratory scale coupled with product analyses and evaluations will enable determination of conditions to be used. Examples 1 and 2 hereinafter provide conditions known to be very satisfactory with the methylaluminoxane solutions used therein.
It will of course be understood that the process of preparing a methylaluminoxane of this invention should be conducted under suitably inert and anhydrous conditions.
The solid methylaluminoxane composition of this invention is the residue formed upon distillation, and thus it has an aluminum content in the range of from about 39 to about 47 wt %, and more preferably in the range of from about 41 to about 45 wt %. Most preferable is an aluminum content in the range of from about 42 to about 44 wt %. Usually the solid methylaluminoxane composition will contain some trimethylaluminum, and when it does, not more than 30 mole %, preferably no more than 20 mole %, and more preferably no more than 10 mole % of the aluminum in the composition is in the form of trimethylaluminum, all as determined by the aforementioned NMR Analytical Procedure. The content, if any, of aromatic hydrocarbon in the compositions of this invention may also conveniently be determined by proton NMR spectroscopy using the aforementioned published NMR Analytical Procedure. In the event of disparate results from different methods of determining the aromatic hydrocarbon content of such compositions, the value as determined by such published NMR procedure should control. The cryoscopic molecular weight of the composition is determined by using benzene, rather than 1,4-dioxane, as the cryoscopic solvent in the procedure described in xe2x80x9cDetermination of Trimethylaluminum and Characterization of Methylaluminoxanes Using Proton NMRxe2x80x9d by Donald W. Imhoff, Larry S. Simeral, Don R. Blevins, and William R. Beard; ppg 177-191 of ACS Symposium Series 749, Olefin Polymerization: Emerging Frontiers; Palanisamy Arjunan, James E. McGrath, and Thomas L. Hanlon, Eds.; copyright 2000 by the American Chemical society, Washington, D.C.
To form the solutions of this invention one either (i) prepares a solid methylaluminoxane of this invention and dissolves all or a portion of such composition in a suitable non-aromatic hydrocarbon solvent, or (ii) if a solid composition of this invention has already been prepared and provided for use, all or a portion of such composition is used in preparing a solution of this invention, or (iii) the methylaluminoxane solution may be prepared directly in the non-aromatic solvent, that is, by reacting trimethylaluminum with a suitable reagent (e.g., water or benzoic acid) in the non-aromatic solvent. Alternative (i) typically involves preparing the solid methylaluminoxane composition (reduced pressure distillation residue) at the site where the solution will be formed. Alternative (ii) typically involves preparing a solid composition of this invention at a plant site which is not necessarily the site at which the solution of this invention will be prepared. In this second case one preparing the solution will typically purchase the solid methylaluminoxane of this invention from the manufacturer thereof. Thus the overall process of this invention (making and dissolving) can be conducted by one party typically at one plant site or by two or more different parties typically at different plant sites (making at one plant site, and dissolving at another plant site). All such alternatives are within the scope of this invention.
Any saturated or unsaturated non-aromatic hydrocarbon, mixture of two or more saturated hydrocarbons, mixture of two or unsaturated non-aromatic hydrocarbons, or mixture of one or more saturated and one or more unsaturated non-aromatic hydrocarbons that exist as a liquid at least throughout the range of about 20 to about 30xc2x0 C. can be used as the solvent in the hydrocarbon solutions of this invention. Preferred hydrocarbon solvents of this type used in the practice of this invention include (a) one or more alkane, alkene, alkadiene, cycloalkane, cycloalkene, cycloalkadiene, or alkyne hydrocarbons, that exist as a liquid at least throughout the range of about 20 to about 30xc2x0 C.; or (b) a mixture of at least two of (a); or (c) at least one of (a) and/or (b), and one or more alkane hydrocarbons that exist as a liquid at least throughout the range of about 20 to about 30xc2x0 C. A few non-limiting examples of such hydrocarbons include n-pentane, isopentane, cyclopentane, 1-pentene, 2-pentene, n-hexane, 2-methylpentane, 3-methylpentane, cyclohexane, 1-hexene, 2-hexene, 3-hexene, cyclohexene, 1,5-hexadiene. methylcyclohexane, n-heptane, 2-methylheptane, 3-methylheptane, 4-methylheptane, 1-heptyne, 2-heptyne, 3-heptyne, n-octane, 1-octene, octadiene, 2,2,4-trimethylpentane, 1,3,5,7-cyclooctatetraene, n-nonane, n-decane, 1-decene, 1-decyne, 5-decyne, xcex1-pinene, decahydronaphthalene, n-dodecane, and pentadecane.
In forming the solutions of this invention, it is desirable that if trimethylaluminum is present in the solid methylaluminoxane composition of this invention being used to form the solution, no more than about 30 mole % of the total dissolved aluminum be present as trimethylaluminum. It is more desirable that no more than 20 mole %, and still more desirable that no more than 10 mole % of the total dissolved aluminum be present as trimethylaluminum, as determined by the aforementioned NMR Analytical Procedure.
Typically, the methylaluminoxane solution has a total dissolved aluminum content above about 4 wt % and more preferably above about 5 wt %. Most preferable is a total dissolved aluminum content which is above about 7.5 wt %. The total dissolved aluminum content is based on the total weight of all dissolved aluminum species which are components of the methylaluminoxane plus the weight of the nonaromatic hydrocarbon solvent. Thus when forming the methylaluminoxane solution the solid methylaluminoxane of this invention is dissolved in a non-aromatic hydrocarbon solvent in amounts such that the methylaluminoxane solution produced contains an amount of dissolved aluminum in accordance with the foregoing. Of course if one wishes to do so, the amount of the solid methylaluminoxane of this invention dissolved in a non-aromatic hydrocarbon solvent can be less than about 4 wt %.
The methylaluminoxane solutions of this invention contain, if any, no more than about 2000 ppm (wt/wt) of aromatic hydrocarbon. Preferably, the solutions contain no more than about 500 ppm, and most preferably no more than about 100 ppm, of aromatic hydrocarbon. The indicated ppm determinations are based upon the total weight of all dissolved aluminum species which are components of the solid methylaluminoxane composition plus the total weight of the hydrocarbon solvent, including aromatic solvent components, if any.
The cryoscopic number average molecular weight, as determined in benzene solution, of the methylaluminoxane in solution is at least about 1000 atomic mass units (amu), preferably above about 1100 amu, and most preferably above about 1200 amu.
When forming the methylaluminoxane solution by the process of the invention, the solid methylaluminoxane composition (e.g., reduced pressure distillation residue) is dissolved in a non-aromatic hydrocarbon solvent in amounts such that the methylaluminoxane solution produced will typically contain at least about 4 wt %, preferably at least 5 wt %, of dissolved aluminum, and more preferably at least about 7.5 wt %. Weight percent of dissolved aluminum is based upon the weight of the solid methylaluminoxane composition (e.g., reduced pressure distillation residue) dissolved in the non-aromatic hydrocarbon solvent, as well as weight of the non-aromatic hydrocarbon solvent.
When the methylaluminoxane compositions and solutions of this invention are hydrolyzed, whether in solid form or in solution, the non-methane hydrocarbon hydrolysis products are the same as those formed from hydrolysis of commercial grades of trimethylaluminum and commercial grades of aromatic-solvent solutions of methylaluminoxanes in that the non-methane hydrocarbon hydrolysis products contain, if any, no more than about 2 mole percent of other hydrocarbons formed during the hydrolysis reaction. Furthermore, they contain essentially no detectable amount of any other hydrocarbon except perhaps at most 2000 ppm (wt/wt) of trace residual amounts of aromatic hydrocarbon (usually toluene) in which the methylaluminoxane had been dissolved before being isolated from such solution. Thus the methylaluminoxane solutions of the present invention are xe2x80x9call-methyl aluminoxanesxe2x80x9d in that they have been produced from trimethylaluminum of standard commercial purity, and no other organoaluminum compound has been added either to the trimethylaluminum used in forming the methylaluminoxane, or to the methylaluminoxane itself. The traces of vaporous hydrocarbon(s) typically, but not necessarily, released on aqueous hydrolysis of the methylaluminoxane probably result from trace amounts of impurities present in the original trimethylaluminum used as the starting material for producing the methylaluminoxane.
The following Examples are presented for purposes of illustration and are not intended to limit, do not limit, and should not be construed as limiting, the generic scope of this invention.
Examples 1 and 2 illustrate methods of producing solid methylaluminoxanes pursuant to this invention.